This research was aimed to explore the effects of blocking B7/CD28 and CD40/CD154 co-stimulatory signals on engraftment of hematopoietic stem cell in the sensitized recipient so as to provide the experimental evidence for the treatment of sensitized recipient's immune rejection after clinical allogeneic hematopoietic stem cell transplantation (HSCT). The BALB/c mice were divided into 4 groups: (1)mice sensitized on 7 day before transplant; (2)mice were sensitized on 7 day before transplant, and injected CTLA4Ig+anti-CD154 applied; (3)normal mice injected by corresponding isotype control IgG of CTLA4Ig and anti-CD154; (4)normal blank control mice. Each group had 15 mice. On day 0, mice of each group were irradiated lethally 8 Gy by linear accelerator, and the bone marrow cells of C57BL/6 labeled by fluorescence staining were injected via the tail vein. The fluorescent cell level in peripheral blood and organ tissue at different time points were detected by flow cytometry (FCM) for homing assessment. Survival rates and hematopoietic reconstitution were also monitored and recorded. The results showed that application of CTLA4Ig anti-CD154 could promote implantation of allogeneic HSC in sensitized recipients, induce the immune tolerance, prolong their survival time and accelerate the hematopoietic reconstitution within 28 days, compared with the sensitized group. It is concluded that applying CTLA4Ig and anti-CD154 can enhance the engraftment of HSCT and induce immune tolerance in the sensitized recipient after allogeneic HSCT and accelerate the hematopoietic reconstitution.